1. Field of the Invention
The present invention generally relates to gallium-nitride based light emitting diodes and, more particularly, to the high-brightness gallium-nitride based light emitting diodes having roughened surfaces.
2. The Prior Arts
Gallium-nitride (GaN) based light-emitting diodes (LEDs), as various colored LEDs can be developed by controlling the GaN-based material's composition, has been the research and development focus in the academic arena and in the industries as well in recent years. One of the research directions regarding GaN-based LEDs lies in the further understanding of the luminous characteristics of GaN-based LEDs. Based on this knowledge, then, methods for enhancing GaN-based LEDs' luminous efficiency and brightness can be developed and discovered. These high-efficiency and high-brightness GaN-based LEDs would soon find their widespread application in outdoor display panels and automobile lamps.
The luminous efficiency of a GaN-based LED is mainly determined by the GaN-based LED's internal quantum efficiency and external quantum efficiency. The former relates to the probability of recombination of electrons and holes, thereby causing photons to be released, within the GaN-based LED's active layer. The more easily the electrons and holes are recombined, the more photons are released, and the higher the luminous efficiency of the GaN-based LED will be. The latter, on the other hand, relates to the probability of photons' successfully escape from the GaN-based LED without being absorbed or trapped inside. The more photons escape from the GaN-based LED, the higher the external quantum efficiency is, and the higher the luminous efficiency of the GaN-based LED will be.
The GaN-based LED's external quantum efficiency is also related to its index of refraction. Generally, the index of refraction of GaN-based LEDs is 2.5, higher than that of the atmosphere (whose index of refraction is 1). As such, total internal reflection would occur and photons released from the active layer would be reflected back to the GaN-based LEDs, significantly reducing the external quantum efficiency.